nanoparticle-sensitized solar cells - northwestern … study... · dye-sensitized solar cell -...
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Nanoparticle-Sensitized Solar Cells
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Dye-Sensitized Solar Cell
•Cost-effective
alternative to silicon
• Lower conversion
efficiency (11%) compared to world record
(~40%)
•Five Basic Steps
•Light Absorption
•Electron Transfer•Electrical Conduction
•Redox Cycle
•Replenish Dye
http://en.wikipedia.org/wiki/Solar_cell#Multiple_junction_solar_cellsGrätzel, M. Nature. 2001, 414, 338.
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Dye-Sensitized Solar Cell - Details
• Injection of electrons from low bandgap to high bandgap
• Nanostructured TiO2 increases surface area• Ruthenium dye increases absorption of device
Grätzel, M. Nature. 2001, 414, 338.Grätzel, M., O’Regan, B. Nature 1991, 353, 737.
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Room for Improvement
Grätzel Cell: • Ruthenium dye has a single absorption energy• Dye has low absorption coefficient• Grain boundaries in TiO2 can impede conduction• Redox couple consists of harsh materials
Nanoparticle Sensitized Cell:• Semiconductor quantum dots have tunable size-dependent absorption• Quantum dots have large absorption coefficient• Possibility for multiple exciton generation (MEG)
Ozin, G. A. Nanochemistry 2005, 268http://nanocluster.mit.edu/wiki/images/f/ff/Vials3.jpg
Bawendi M. G. et al. J. Am. Chem. Soc. 1993, 115, 8706
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Quantum Dot Sensitized Cell
Kamat, P.V. et al. J. Am. Chem. Soc. 2006, 128, 2385.
• Conjugate CdSe Quantum Dots (~3nm) to TiO2
nanoparticles (40-50nm)• Determine extent of electron transfer from excited quantum dots (Eg=2.25 eV)
to TiO2 (Eg=3.44 eV)
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Probing Electron Dynamics
Kamat, P.V. et al. J. Am. Chem. Soc. 2006, 128, 2385.
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Size Dependent Electron Transfer
Kamat, P.V. et al. J. Am. Chem. Soc. 2007, 129, 4136.
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Improved Performance
• Changes in TiO2 morphology affects electrical conduction
• Optimum quantum dot size balances high electron transfer rate with broad absorption in visible spectrum
• IPCE value of 45% and power-conversion efficiency of 1%
Kamat, P.V. et al. J. Am. Chem. Soc. 2008, 130, 4007.
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Conclusions
• Significant room for improvement in quantum dot sensitized
systems
• Understanding of nanoparticle sensitized solar cells remains at the level of fundamental investigations
• Considerable materials science challenges remain:
• Synthesis of complex, multicomponent nanostructures
• Band gap engineering for optimum conversion efficiency
• Incorporation of multiple exciton generating quantum dots